Added skeleton loading paradigm to UX guide

doc/development/ux_guide/animation.md

@@ -39,6 +39,12 @@ When information is updating in place, a quick, subtle animation is needed. The
 
 ![Quick update animation](img/animation-quickupdate.gif)
 
+### Skeleton loading
+
+Skeleton loading is explained in the [component section](components.html#skeleton-loading) of the UX guide. It includes a horizontally pulsating animation that shows motion as if it's growing. It's timing is a slower `linear 1s`.
+
+![Skeleton loading animation](img/skeleton-loading.gif)
+
 ### Moving transitions
 
 When elements move on screen, there should be a quick animation so it is clear to users what moved where. The timing of this animation differs based on the amount of movement and change. Consider animations between `200ms` and `400ms`.
@@ -51,7 +57,9 @@ View the [interactive example](http://codepen.io/awhildy/full/ALyKPE/) here.
 ![Reorder animation](img/animation-reorder.gif)
 
 #### Autoscroll the page
+
 Another example of a moving transition is when you have to autoscroll the page to keep an active element visible.
 
 View the [interactive example](http://codepen.io/awhildy/full/PbxgVo/) here.
+
 ![Autoscroll animation](img/animation-autoscroll.gif)

doc/development/ux_guide/components.md

@@ -204,6 +204,25 @@ Cover blocks are generally used to create a heading element for a page, such as
 
 ---
 
+## Skeleton loading
+
+Skeleton loading is a way to convey to the user what kind of content is currently being loaded. It's a paradigm with which content can independently and asynchronously be loaded, while still adhering to the structure and look of the completely loaded view.
+
+### Requirements
+
+* A skeleton should represent an organism in a recognisable way
+* Atom elements within organisms (for reference see this article on [atomic design methodology](http://atomicdesign.bradfrost.com/chapter-2/)) may be represented in a maximum of 3 repetitions, if applicable.
+* Skeletons should only be presented in grayscale using the HEX colors: `#fafafa` or `#ffffff` (except for shadows)
+* Animate the grey atoms in a pulsating way to show motion, as if "loading". The pulse animation transitions colors horizontally from left to right, starting with `#f2f2f2` to `#fafafa`.
+
+![Skeleton loading animation](img/skeleton-loading.gif)
+
+### Usage
+
+Skeleton loading can replace any existing UI elements for the period in which they are loaded and should aim for maintaining a similar structure visually.
+
+---
+
 ## Panels
 
 > TODO: Catalog how we are currently using panels and rationalize how they relate to alerts